<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
  <style>
    #outer{
      height: 400px;
      width: 400px;
      background: gray;
    }
    #inner1{
      background: red;
      margin: 100px;
    }
    #inner2{
      background: green;
      /*margin: 100px;*/
    }
    #inner3 {
      background: yellow;
      /*margin: 100px;*/
    }


  </style>
</head>
<body>
<div id="outer">
  <div id="inner1">inner1</div>
  <div id="inner2">inner2</div>
  <div id="inner3">inner3</div>
</div>
</body>
</html>